From PhysOrg:
The research, published online, ends a 30-year search for the most efficient way to correctly align the 26 colored cubes that make up Erno Rubrik's 1974 invention. “It took fifteen years after the introduction of the Cube to find the first position that provably requires 20 moves to solve,” the team said. “It is appropriate that fifteen years after that, we prove that twenty moves suffice for all position.” Using computers lent to them by Google — the company won't disclose how many or how powerful they are — the team crunched through billions of Cube positions, solving each one over a period of “just a few weeks.”
The study builds on the work of a veritable pantheon of Rubik's researchers, starting with Morwen Thistlethwaite who in 1981 showed 52 moves were sufficient to reach the solution from any given Cube position. By May 1992, Michael Reid showed 39 moves was always sufficient, only to be undercut a mere day later by Dik Winter, who showed 37 moves would work. Rubik's enthusiasm extends not only to God's number, but the speed with which the tricky puzzle can be solved. The current world record holder is Dutch Erik Akkersdijk who successfully solved the puzzle in just 7.08 seconds.
More here.
